The political positions taken up after the Las Vegas massacre are too familiar.

Democratic leaders, such as U.S. Sens. Chris Murphy, D-Connecticut, and Amy Klobuchar, D-Minnesota, immediately called for new gun control measures. They say they want, at the very least, to close loopholes in the national firearm background check system.

And most Republicans, from statehouses right through to the White House, say they don’t want new gun control laws. Kentucky Gov. Matt Bevin seemed to distill this view with a tweet noting, “You can’t regulate evil.”

[I used to think gun control was the answer. My research told me otherwise.]

This playing-out of political roles seems to happen after every mass shooting, like it’s part of the program. It has occurred after incidents in Aurora, Colorado, and Newtown, Connecticut, and San Bernardino, California, and Orlando. On and on.

But one reason the positions are so intractable is that no one really knows what works to prevent gun deaths. Gun-control research in the United States essentially came to a standstill in 1996.

After 21 years, the science is stale.

“In the area of what works to prevent shootings, we know almost nothing,” Mark Rosenberg, who, in the mid-1990s, led the CDC’s gun-violence research efforts, said shortly after the San Bernardino shooting in 2015.

[America’s gun debate needs reason, common sense, high-quality research]

In 1996, the Republican-majority Congress threatened to strip funding from the Centers for Disease Control and Prevention unless it stopped funding research into firearm injuries and deaths. The National Rifle Association accused the CDC of promoting gun control. As a result, the CDC stopped funding gun-control research — which had a chilling effect far beyond the agency, drying up money for almost all public health studies of the issue nationwide.

The National Institute of Justice, an arm of the U.S. Department of Justice, funded 32 gun-related studies from 1993 to 1999, but none from 2009 to 2012, according to Mayors Against Illegal Guns. The institute briefly resumed some funding in 2013 and 2014, in the wake of the Sandy Hook Elementary shooting in 2012, but has made no grants since then. Researchers in search of private funding say they know to avoid the word “gun” or “firearm” in the titles of violence-prevention studies to avoid blowback.

[This is the deadliest mass shooting in modern US history. How should we talk about it?]

That hasn’t stopped the rallying cry for “common-sense gun control.” But, as Rosenberg pointed out, we don’t know what that looks like. Maybe background checks are not the answer. Maybe allowing guns on college campuses makes those places safer. Maybe there is a way to stop a single gunman from killing and wounding hundreds of people at a concert in Las Vegas.

But, many advocates say, it’s impossible to have an honest debate about preventing gun violence when we can’t study the issue.

Everyone agrees the Las Vegas shooting was a tragedy. But no one knows what might work to prevent the next one.

“If we get better data, we could get a lot of traction on this,” said Jennifer Doleac, an assistant professor of public policy at the University of Virginia, who has used gunfire-detection technology deployed in many cities to study how often guns are fired. “It’s just so political.”

Jay Dickey was a Republican congressman from Arkansas who, in the mid-1990s, led the effort to stop the CDC’s gun violence research. The Dickey Amendment, as it’s known, has been reauthorized every year by Congress. He and Rosenberg, the former CDC official, were once sworn enemies. But the two men later became friends. And Dickey, before he died earlier this year, changed his thinking. After the successive waves of mass shootings, he saw that something needed to be done. Dickey said he changed his mind: Gun violence needed to be studied by the CDC. He wanted solutions — ones that, he said, also protected gun rights. It might be possible.

“We need to turn this over to science and take it away from politics,” Dickey said.

All he wanted to do was find out.